Multilayer films prepared from polycarbonates and polycarbonate blends have useful properties such as weatherability, scratch resistance, and high gloss, and can be used as surface finish layers for molded articles. Further, where one or more layers of these multilayer films are used to carry a colorant and/or other additives for obtaining visual effects for the article, the multilayer films are useful as paint-replacement layers for molded articles. Articles for which such multilayer films are useful include automotive applications, horizontal applications such as outdoor applications, including sauna covers, pool covers, lawn and garden furniture, rooftops, deck lids, exterior panels, and the like.
A multilayer film can be back molded with a substrate material, such as polyurethane foam, for example, which provides mechanical support and other properties for the multilayer film. The substrate may be a thermoset or a thermoplastic material, as selected. To provide adhesion between the multilayer film and substrate, the multilayer film can be constructed with one or more intermediate layers, referred to as a “tie layer” or “tie layers”, that are useful for providing thermal stability as well as adhesion between the superstrates having the surface finish properties, and the substrate.
Tie layers that are adequate for applications such as those described above may nevertheless not be suitable for newer applications with different geometries, different processing conditions and/or different substrate materials. Newer applications for which tie layers with different, improved thermal and mechanical properties are beneficial include, for example, those produced via profile extrusion, sheet extrusion, blow molding, thermoforming, and other processes known in the art, where the composition is exposed to higher temperatures for longer periods of time. Processes like profile extrusion, sheet extrusion, blow molding and thermoforming require materials and films having greater thermal stability, higher modulus and good flow and impact balance. In addition, present tie layers having low modulus often do not age well and therefore are likely to become brittle over time. Low modulus materials do not transfer stress without excessive deformation and therefore are often not suitable for mechanical applications.
There accordingly remains a need in the art for a tie layer composition suitable for preparing a tie layer having improved thermal and mechanical properties as well as good adhesion to other layers in the multilayer film as well as the substrate.
A tie layer prepared using the tie layer composition also desirably provides a lower defect rate, particularly with regard to surface defects, and a better balance of properties such as impact and flow, than that obtained with the currently used tie layer compositions.